1. Field of the Invention
The present invention concerns surgical instruments for moving one part of a surgical implant into adjacent position or contact with another. In particular, the invention contemplates rod reducer instruments for use in placing or moving an orthopedic rod toward a bone fixation element.
2. Description of the Related Art
In orthopedic surgery, and particularly in spinal surgery, it is well known to correct an injury, malformation, or other defect using an implanted rod affixed to a body part to be corrected. For example, rod systems have been developed for correcting the positioning of and stabilizing of the spine, and for facilitating fusion at various levels of the spine. In one such system, the rod or elongated implant can be disposed longitudinally along a length of the spine. The rod can be bent, either prior to or during surgery, to correspond to the normal curvature of the spine in the particular region being instrumented, or to such other curvature as the surgeon may deem appropriate to correct the defect. For example, the rod can be bent to form a normal kyphotic curvature for the thoracic region of the spine, or to form a normal lordotic curvature for the lumbar region. The rod can then be attached or engaged to a number of fixation elements which have been inserted or implanted into the vertebrae along the segment of the spinal column.
Fixation elements are well know in the art and can include all types of bone screws, hooks, bolts, etc. configured to engage the vertebrae. For instance, one such fixation element is a laminar hook, configured to engage a lamina of the vertebra. Another prevalent fixation element is a spinal screw which can be threaded into a pedicle or other portion of vertebral bone. An alternative type of fixation element is a multi-axial bone screw.
In one typical spinal procedure, a rod is coupled to two or more bone screws that are fixed to opposite sides of the spine or spinous processes. The bone screws are first threaded into a portion of several vertebral bodies, such as the pedicles of these vertebrae. The rod is coupled to the bone screws to provide corrective and stabilizing forces to the spine. Affixing a rod to a bone screw generally requires the rod to be in close adjacent position or in contact with the screw. This may require that the rod and implanted bone screw be moved with respect to each other so that the rod occupies space within a channel or other opening in the screw. The rod can then be coupled to the implanted bone screw using a set screw, plug or other appropriate fastener. The process of placing a rod within or adjacent to an implanted fixation element so that they can be coupled together is termed “reducing” the rod.
Rod reduction is commonly performed by a surgeon using his or her hands and/or rigid tools such as pliers, levers or other instruments able to create the necessary pushing and/or pulling forces on the implanted fixation element and rod. Such procedures generally require the surgeon to place the rod directly over the implanted fixation element, intersecting a longitudinal axis of the fixation element. Consequently, access to the rod and the implanted fixation element along that axis, i.e. directly above the opening in the fixation element into which the rod is to be placed, can be necessary or at least highly desirable. However, such access can be difficult depending on such factors as the malformation to be corrected and the overall physiology of the patient. Additionally, as surgical procedures are generally encouraged to be minimally invasive, access can be very difficult as a result of the small ports or incisions of such procedures. Additionally, with use of mono-axial screws, the physiology of the patient can require that the screw be placed at an angle such that the surgeon would have difficulty accessing and exerting force in the necessary orientation on the rod and/or fixation element. With multi-axial fixation devices, the orientation of an unsecured rod-receiving part of the fixation element can be even more varied with respect to the rod and/or the surgeon. Consequently, the surgeon is still frequently faced with the task of reducing a rod from an awkward angle.
Various attempts in the prior art have been made in providing rod reducing instruments, for example, the rod reducer instrument disclosed in U.S. Pat. No. 6,790,209 to Beale. The rod reducer of Beale utilizes a pliers arrangement to reduce a rod. Rod reducing pliers of this type can be difficult to use as the amount of pressure required to reduce the rod may depend on the particular fixation element and rod and may be difficult for particular users without great hand strength. Therefore there exists a need for a more efficient and easier to use rod reducing instrument that can be used efficiently, safely and securely in rod reduction procedures and for rod reduction instruments that can be used in both minimally invasive and open surgical approaches to the site of rod attachment.